The rules state that when you begin construction on a Space Station, you are free to move around as well as you don't need to stay with the NPC builders. I'm assuming that if all materials and NPC's were aboard one ship, after starting construction, you can leave.

In facility construction, the NPC's are on the ground. So the builders building a Space Station are theoretically on the Station while constructing it? (I just want to make sure I don't have to leave another ship at the construction location for the builders.)

Apart from the obvious functions of some, stations can generally be used to dock ships (of appropriate size), used for storage (again, dependent on size) and many offer NPCs for hire without the hassle of going to a planet surface.

No, they don't. They need to be there BEFORE you start construction, obviously. But once you start it they are removed from their containers and added to the construction task. Just like facility construction. You don't need to leave the ships there for the RMs.

Uhhh...one last question, sorry for taking over the thread again but say you are attempting to build an SY 4 now obviously the amount of mats needed won't fit in one bulk and say that you only have bulks (2 or 3); can you build it if all 3 ships have the necessary amount of mats?

You can split the necessary RMs over as many ships as you want, as long as they are all in the same location as the SY is to be built. NPCs should be on the same ship as the person starting construction, and I believe the person starting construction needs to be on the crewlist of all the ships.